Between two solutions separated by a semipermeable membrane, the solvent moving from the solution with a low solute concentration to the solution with a high solute concentration by passing through the membrane is referred to as osmosis, and herein, the pressure applied to the solution with a high solute concentration caused by the solvent migration is referred to as an osmotic pressure. However, when applying an external pressure higher than an osmotic pressure, the solvent migrates to the solution with a low solute concentration, and this phenomenon is referred to as reverse osmosis. Using a reverse osmosis principle and with a pressure gradient as a driving power, various salts or organic materials may be separated through a semipermeable membrane. A water-treatment membrane using such a reverse osmosis phenomenon separates molecular-level materials and removes salts from salt water or sea water, and is used to supply water for domestic use, construction, and industrial use.
Typical examples of such a water-treatment membrane may include a polyamide-based water-treatment membrane, and the polyamide-based water-treatment membrane is manufactured using a method of forming a polyamide active layer on a microporous support layer, and more specifically, is manufactured using a method of forming a microporous support by forming a polysulfone layer on a nonwoven fabric, forming a mPD layer by immersing this microporous support into an aqueous m-phenylenediamine (mPD) solution, and forming a polyamide layer through interfacial polymerization by immersing this again in a trimesoyl chloride (TMC) organic solvent to bring the mPD layer into contact with the TMC.
Flux and salt rejection are used as important indexes representing membrane performance in the water-treatment membrane.